1. Field of the Invention
The present invention relates generally to a container suitable for use in a hot-fill process, and more particularly to a container with a dome having a waist and no reinforcing ribs and the container having a circumferential ring that can be located under a label.
2. Related Art
Blow-molded plastic containers have become commonplace in packaging beverages and other liquid, gel, or granular products. While a container may provide an appealing appearance when it is initially removed from blow-molding machinery, many forces act subsequently on, and alter, the shape from the time it is blow-molded to the time it is placed on a shelf in a store. Plastic containers are particularly susceptible to distortion after hot-filling and capping when design changes are implemented to reduce the amount of plastic required to make the container. While there is a savings with respect to material cost, the reduction of plastic can decrease container rigidity and structural integrity.
In the packaging of beverages, for example juices, blow-molded plastic polyethylene terephthalate (PET) containers are commonly used in hot-fill processes. In the hot-fill process, a container is filled with a product at an elevated temperature, sealed and allowed to cool. Several internal forces act on the container during hot-fill processing. For example, when the heated product is added, softening of the plastic can occur that can tend to cause distortion. As the container and the contained product cools, a partial vacuum is created inside the container, placing forces on the container that can cause it to partially collapse. Hot-fillable plastic containers must provide sufficient flexure to compensate for the changes of pressure and temperature, while maintaining structural integrity and aesthetic appearance. The flexure is most commonly addressed with vacuum flex panels positioned under a label below the dome.
In addition to internal forces, external forces are applied to sealed containers as they are packed and shipped. Filled containers are packed in bulk in cardboard boxes, or plastic wrap, or both. A bottom row of packed, filled containers may support several upper tiers of filled containers, and potentially, several upper boxes of filled containers. Therefore, it is important that the container have a top loading capability which is sufficient to prevent distortion from the intended container shape.
Dome region ovalization is a common distortion associated with hot-fillable, blow-molded plastic containers. The dome is the upper portion of the container adjacent the finish. Some dome configurations are designed to have a horizontal cross-section which is circular in shape. The forces resulting from hot-filling and top loading can change the intended horizontal cross-sectional shape, for example, from circular to oval.
FIG. 1 illustrates a blow-molded plastic container 100 according to the prior art that has features common to other known containers. For instance, the container 100 has a finish 102 which provides an opening 104 for filling and subsequent emptying of the container contents, as well as for receiving a closure (not shown). A dome 106 extends from the finish 102 to a circumferential ring 108. The circumferential ring 108 is preferably located in the shoulder of the container just below the dome 106. The circumferential ring 108 has a concave structure, the concavity being an arc with a relatively small radius. It is also preferred that the arc sweep out a significant angle. The curvature of the concavity together with its extent and depth allow the circumferential ring 108 to provide structural support to prevent shape distortion of the container, particularly in preventing ovalization of the container sidewalls and/or dome 106. Particular dimensional properties of the arc that defines the circumferential ring providing the necessary rigidity are known in the art and given in, for example, U.S. Pat. No. 5,303,834, which is incorporated herein by reference in its entirety.
An upper label bumper 110 is located below the circumferential ring 108. The container 100 has a base 112 which is located remote from the finish 102 and which extends to a lower label bumper 114. The lower label bumper 114 and upper label bumper 110 define the extent of a label mounting area 116. The label mounting area 116 has a series of spaced-apart vacuum flex panels 118 which accommodate volumetric changes to a hot-filled container after it has been sealed and as it cools.
The dome 106 of the container illustrated in FIG. 1 has a bell-shaped profile and a substantially circular horizontal cross-section. In this example, the horizontal cross-section through the dome 106, starting from beneath the finish 102, increases in diameter in an upper dome portion as it extends toward the base 112, decreasing to form the circumferential ring 108. Below the circumferential ring 108, the container diameter increases to the upper label bumper 110.
Although the circumferential ring 108 resists ovalization and assists in maintaining the structural integrity of the container, as efforts are made to lightweight plastic containers, vacuum forces will act on thin regions susceptible to distortion causing disfiguration of the container. One region that is particularly susceptible to such forces is the dome. The dome represents a relatively large open area that may have little in the way of support structure. To provide support for the dome under vacuum forces, structural features can be added to the dome to provide reinforcement. For example, U.S. Pat. No. 5,762,221 of common assignee, which is incorporated herein by reference in its entirety, describes the use of reinforcing ribs 125 to provide structural support to the dome 106. The reinforcing ribs, which may either extend into or out from the container, interrupt the generally circular cross section. Such a design allows for an adequately large logo presentation area 120 when the container is of sufficient size, for example a container designed to hold about 32 ounces of a fluid product. However, as the container size decreases, for example to hold about 20 fluid ounces or less, the logo presentation area 120 also decreases in size as the reinforcement ribs 125 become closer together. This reduction in size of the logo presentation area can be undesirable to the commercial manufacturers of products packaged in the containers.
FIG. 2 illustrates another prior art approach that provides a container 200 having a dome 206 with top load strength and resistance to ovalization. The dome 206 of this design does not have any ribs, but is substantially conical in shape. The conical shape provides sufficient top load strength and resistance to ovalization to be commercially viable. However, even in this configuration, the size of the logo presentation area 220 is reduced due to the tapering of the dome 206, and can be less than what is commercially desirable.
While features such as a circumferential ring and reinforcing ribs provide structural support to the dome, use of these features imposes restrictions on the design of containers. These restrictions limit the ability to incorporate features that may be important commercially to manufacturers of products packaged in the containers. For example, the use of reinforcing ribs 125 limits the open areas of the dome that may the used for a logo presentation area. These open areas can be sufficiently large to hold a product logo in containers designed to contain relatively large amounts, for example 32 ounces, of liquid; however, as the size of the container is reduced, the logo presentation area necessarily decreases in size to accommodate space for the ribs 125. Moreover, because the circumferential ring is used as a reinforcing structure for the dome, it must generally be located relatively close to the dome and is typically adjacent to the dome. Due to the proximity of the circumferential ring to the dome, it is most often located above the upper bumper and outside of the label mounting area so that it is visible in the final packaged product. Additionally, the circumferential ring must have a concavity that is sufficiently arcuate to provide structural support to the dome. These features, i.e. reinforcing ribs and/or a circumferential ring, which are required to maintain structural integrity of prior art hot-fill containers, reduce the ability to design containers that do not contain a visible waist or reinforcing ribs outside the label mounting area or that have a sufficiently large uninterrupted dome for placement of a logo.
Although containers having a specific dome configuration may function satisfactorily for their intended purposes, there is continuing need for blow-molded plastic containers having a dome which controls the amount of ovalization distortion due to hot-filling, and resists compressive distortions due to top loading. Such a container is desirably made from a minimal amount of plastic to afford efficient manufacture. Incorporating an aesthetically pleasing appearance while being able to maintain structural integrity of the container during the hot-fill process remains a challenge.